Numerous methods have been employed to separate connecting rod preforms by fracturing, both in laboratory and production environments. These include cryogenic cooling or electron beam exposure to era brittle the fracture area, fracturing by wedge actuation of an expanding mandrel, and linear opposing pulling forces to separate the bearing cap from the connecting rod preform. The following patents are representative of the prior art:
U.S. Pat. No. 4,569,109, issued on Feb. 11, 1986; PA1 U.S. Pat. No. 4,768,694, issued on Sep. 6, 1988; PA1 U.S. Pat. No. 4,993,134, issued on Feb. 19, 1991. PA1 (a) achieving simultaneous fracture along the cracking plane of both legs of the connecting rod. Failure to achieve simultaneous fracture is likely to result in plastic deformation of the crank bore and inhibit re-mating of the two parts; PA1 (b) maintaining positive control over the position of the separated bearing cap and connecting rod body, to ensure accurate micro-alignment during re-mating. Failure to do this may negate the inherent advantages of fracture separation. PA1 a base member, PA1 a guide member fixed with respect to said base member, the guide member defining a first guideway extending in a first direction, PA1 a first slide member mounted to said guide member for sliding movement along said first guideway in said first direction, the first slide member defining a second guideway also extending in said first direction, PA1 a second slide member mounted to said first slide member for sliding movement with respect to said first slide member along said second guideway in said first direction, PA1 a mandrel which is split to define an upper pan fixed with respect to the first slide member and a lower part fixed with respect to said base member, said upper part being movable between a first position in which it is spaced away from the lower pan and a second position in which it is juxtaposed against the lower part to define a substantially cylindrical body having its axis lying substantially in a second direction perpendicular to said first direction, movement of said upper part being simultaneous with movement of the first slide member along the first guideway with respect to said guide member, the upper and lower parts of said mandrel defining an internal tapered passageway, PA1 a wedge member adapted, when the upper part is in its second position, to enter said tapered passageway and force said mandrel pans apart, PA1 power means for moving said wedge member, PA1 projections defined by said second slide member and adapted to contact the bolt seat shoulders of an integral preform while the cylindrical aperture thereof receives the split mandrel, and PA1 means for selectively urging the second slide member toward the mandrel, thereby securely holding the integral preform in place, PA1 whereby the wedge member can enter the tapered passageway, forcing the mandrel parts apart and fracturing the preform into a bearing cap and a connecting rod. PA1 a) fitting the cylindrical aperture of the preform over a substantially cylindrical mandrel which includes separate upper and lower parts, PA1 b) holding the preform in place over the mandrel by pressing against the bolt seat shoulders in the direction toward the mandrel, and PA1 c) forcing the mandrel parts apart while holding the preform in place, thereby to fracture the preform into a bearing cap and a connecting rod.
Despite these prior developments, certain elements vital to fracture separation continue to have the greatest influence on the quality of the finished connecting rod. Two of these elements are: